Metallized plastic part and process for its production

ABSTRACT

A PLASTIC PART CONSISTS OF AN ACRYLONITRILE, BUTADIENE AND STYRENE RESIN. IT IS COVERED WITH A SERIES OF METAL LAYERS TO PROVIDE AN ADHERENT METAL COATING. THE FIRST LAYER IS REDUCED METAL, SUCH AS COPPER; THE SECOND LAYER IS STRESS-FREE NICKEL; THE THIRD LAYER IS AN ELECTOLYTICALLY DEPOSITED METAL OTHER THAN COPPER, SUCH AS BRIGHT NICKEL; AND THE FOURTH LAYER IS ELECTROLYTICALLY PLATED CHROME. THE PLASTIC PART IS DIPPED IN A CONDITIONER OF PHOSPHORIC AND MOLYBDIC ACIDS, REMOVED FROM THE CONDITIONING BATH AND SUBSEQUENTLY HEATED PRIOR TO ITS BEING COATED WITH THE METAL LAYERS.

Feb. 23', 1971 w, YOUNG ETAL METALLIZED PLASTIC PART AND PROCESS FOR ITS PRODUCTION Filed May 28, 1965 INVENTORS.

w s n u H N wwm J m hu n w A M m b M50 WBJ United States Patent 3,565,770 METALLIZED PLASTIC PART AND PROCESS FOR ITS PRODUCTION William H. Young, Trumbull, Bela Csuthy, Prospect, and Joseph Guidess, Watertown, Conn., assignors to Timex Corporation, a corporation of Delaware Filed May 28, 1965, Ser. No. 459,544 Int. Cl. 'C23b 5/60 US. Cl. 204-30 4 Claims ABSTRACT OF THE DISCLOSURE A plastic part consists of an acrylonitrile, butadiene and styrene resin. It is covered with a series of metal layers to provide an adherent metal coating. The first layer is a reduced metal, such as copper; the second layer is stress-free nickel; the third layer is an electrolytically deposited metal other than copper, such as bright nickel; and the fourth layer is electrolytically plated chrome. The plastic part is dipped in a conditioner of phosphoric and molybdic acids, removed from the conditioning bath and subsequently heated prior to its being coated with the metal layers.

This invention relates to an improved metallized plastic part and the process for producing it. It has special reference to watch parts and particularly to a watch case, including a bezel and back.

A commercially useful watch bezel or back (or other part) must be produced economically, of course, and must have good adhesion between the metal and plastic; and the top layer of a watch bezel or back must have a jewelry finish in order to be aesthetically acceptable. Our invention achieves these desirable characteristics, as well as permitting the use of thinner metal plate layers than previously used in the plating of plastics.

The metallizing of plastics has been proposed at least as early as 1936 (see, for example, US. Pat. No. 2,063,- 034). Various methods for the metallizing of plastics are described in the book by Harold Narcus entitled Metallizing of Plastics (Reinhold Publishing Corporation, 1960). Chapter 2 of that book is devoted to the deposition of metallic coatings by chemical reduction. As shown in chapter 2 of that book, it is known to metallize a plastic part by chemical treatment of it to receive a deposit of a metal, such as copper, on the plastic, by reduction of the metal from a bath containing a salt of the metal in which the plastic is immersed, and thereafter to apply an electrolytic coating or coatings of metal. The principal steps of chemical treatment prior to the deposition of the reduced metal involve essentially the steps of conditioning, sensitizing and activating the plastic as more fully shown in that book and in the prior art, for example US. Pats. Nos. 2,063,034 and 2,454,610. Some years ago, there was developed a polymer based on acrylonitrile, butadiene and styrene of the so-called Type G. Such resins of that Type G are more fully described in the book ABS Plastics (Reinhold Publishing Corporation, 1964). Such a type of resin has been recommended by its producers for use in making electroplated plastic parts.

We have found that, in the process of using such an ABS resin, after deposition of the reduced metal layer and before deposition of a 'final layer or layers by electrolytic means, a substantially improved product results from the deposition between these last two steps of a nickel layer which is substantially stress-free. This layer is applied by using a conventional electroplating technique from a bath containing a substantially stress-free nickel salt, such as nickel sulfamate.

The production of such an improved part consists essentially of molding such an ABS resin in the desired shape, chemically conditioning it, sensitizing it and activating it and thereafter immersing it in a bath containing a metallic salt which is deposited on the part upon reduction of the metal. In accordance with our improved method, the part is then coated with a layer of substantially stress-free nickel by electrolytic deposition of nickel from a bath consisting basically of nickel sulfamate or other substantially stress-free nickel salt. Thereafter an additional layer or layers of metal, as desired, may be applied by conventional electrolytic deposition. Another feature of our invention is an improved solution for conditioning the plastic; and still another feature is a method of heat conditioning the plastic after the step of activation and before deposition of any reduced metal layer, all as more fully shown hereinafter in Example II.

The ABS resin for use in carrying out our invention may contain reinforcing agents such as glass fibers. A watch bezel and back (which may be separate from or an integral part of the bezel) produced through use of this improved method has excellent adherence between the plastic and metal and has a fine jewelers finish which is necessary in order for the part to be commercially acceptable for use. We have found that use of our improvement also permits use of substantially thinner metal layers than previously used. For example, in the plating of plastics after the reduced metal layer, an electrolytically deposited layer of copper on the order of .003 of an inch in thickness was commonly applied. Our improvement permits the use of such an intermediate layer (applied before the last metal layer) of less than one-half such thickness. In addition, our improvement permits the elimination of such an electrolytic copper layer. The elimination of copper in a watch bezel and back is very important since the skin of some wearers is affected by contact with a watch case containing copper, and tarnishing from the formation of copper oxides may result, even though the copper is overlaid with other metal layers.

Where our improvement is used in making a watch bezel or back, after deposition of the stress-free nickel layer, we prefer thereafter to add by electrolytic deposition a bright nickel layer before the final metallic layer. This nickel layer and the stress-free nickel layer generally will not exceed .0015 of an inch.

In the accompanying drawing, FIG. 1 is a perspective view of a watch bezel 1, and FIG. 2 of a watch back 10, each having a base of plastic comprised of a Type G acrylonitrile, butadiene and styrene (a so-called ABS resin) and having additional layers thereon of reduced metal, a stress-free nickel layer and a final electrolytically deposited layer.

In FIG. 3 a cross section of the watch bezel of FIG. 1 along 33, is shown.

The plastic base of watch bezel 1 is 2, the reduced metal layer is 3, the stress-free nickel layer is 4 and the final electrolytically deposited layer or layers is 5. Not shown is the bright nickel layer which we prefer to use in making a watch bezel or back. Such a layer would be included between the stress-free nickel layer 4 and the final layer or layers 5.

The following examples further illustrate our invention.

EXAMPLE I A watch bezel was molded from a Type G acrylonitrile, butadiene and styrene resin and designated as Cycolac A.B.S. (EP3510). The bezel was cleaned in a covered basket by ultrasonic vibration in a 10% oakite liquidet solution in distilled water at a temperature of 150160 F. The part was then rinsed well in clean water and permitted to drain.

The plastic bezel was then conditioned by immersion in a solution of distilled water containing 600 ml. of sulfuric acid (SP. G. 1.84) for each liter of water and about 15 grams of potassium dichromate for each liter of water. The solution was maintained at a temperature of 110 F. and the plastic part was immersed for about 10 minutes. The plastic bezel was then rinsed in water and drained and immersed for a minute in a room temperature solution of distilled water containing 15 grams of stannous chloride for each liter of water, and about 8 ml. of hydrochloric acid, SP. G. 1.15, for each liter of water. The part was then rinsed in water and allowed to drain and then immersed for one minute in a solution of distilled water at room temperature containing 1 gram/ liter of gold chloride and ml./liter of hydrochloric acid (SP. G. 1.15). It was then rinsed in water and permitted to drain. Thereafter it was plated with a layer of about .000002 of an inch of reduced copper by immersion for about 20 minutes at room temperature in an electroless copper bath containing one part of deionized water, one part of Cu 400'A, a copper salt solution sold by Enthone, Inc., and one part of Cu 400-B, a reducing agent sold by that company.

Alternatively, the part may be given a layer of electroless nickel by immersion for about 5 minutes in a bath using distilled water and the following composition:

Grams/liter Nickelous ammonium sulfate 20 Potassium aluminum sulfate Sodium citrate 10 Sodium acetate 10 Sodium hypophosphite 10 Temp. 150 to 160 F. Use distilled water.

We prefer to use the electroless copper solution.

The part was then rinsed and allowed to drain and dried for minutes at about 130 F.

The bezel was then given a layer of about .0003 of an inch of stress-free nickel by electroplating using sulfur depolarized nickel anodes at a temperature of 100 to 120 F. and pH of 3-5 from a nickel sulfamate solution, having the following composition:

Concentration: Compound 40-45 ozs./ gal. Nickel sulfamate. 5-6 ozs./gal. Boric acid.

.25% by volume Lea RonalNW wetting. .05 by volume Lea RonalN222 (Brightner). .05% by volume Lea RonalBeta (Brightner).

Thereafter an electro bright nickel plate of from .0009 to .0012 of an inch thickness was applied by electrolytic deposition from a Lea Ronal N222 Bath. The part was then rinsed and given a plate of chrome by immersion for 3 minutes in a conventional chrome plating bath to give a final layer of chrome of about .00001 of an inch in thickness.

To test the adhesion of the metal layers to the plastic of the product made according to the foregoing Example I, it was heated for two hours at a temperature of 180 F. and then cooled and held at F. for two hours. After four cycles of such heating and cooling the part, there was no lifting, cracking or flaking of the metal layers.

EXAMPLE II A plastic watch bezel having an integrated back was molded of the same material specified in Example I. It was then given coatings of metal layers using the same procedure specified in Example I except that the bezel was conditioned in a solution made by adding together 30 grams of potassium dichromate, 450 ml. of sulfuric acid (SP. G. 1.84), 10 grams of molybdic acid in 200 ml. of water and 350 ml. of phosphoric acid The part was immersed in the conditioner at a temperature of about F. for about 10 minutes.

After the activation step as in Example I, the plastic part was heated at a temperature of 130 F. for two hours, ie after the gold chloride and rinsing steps.

We have found that either of the foregoing modifications shown in Example II give improved results over a part treated as in Example I, and that use of the combination of such modifications produce a metallized plastic part which passes 10 cycles of the heating test specified above.

The use of the combination of phosphoric acid and molybdic acid permits a higher concentration of the dichromate without its precipitation and gives a better etch to the plastic part. Where only about 15 grams/liter of dichromate may be used without that combination, 30 grams may be used if the phosphoric acid and molybdic acid are present.

In using our improved conditioner we have found that use of about 200 ml. to about 350 ml. of phosphoric acid (85%) is desirable in each liter of water (including water from all sources and that included with the phosphoric solution). As to the molybdic acid, it is desirable to use (calculated on the basis of the oxide M00 from about 5 to about 10 grams/liter of water.

The conditioner should be used at a temperature of about 130 to about F., and the part should be immersed in it for about 5 to about 15 minutes.

-' have found that it is desirable to condition the plastic after activation at a temperature of from about 130 to about 240 F. at a time of about 2 to about 24 hours.

We claim:

1. In the process of rnetallizing a plastic part comprised of an acrylonitrile, butadiene and styrene resin by the steps of chemically conditioning, sensitizing and activating said plastic part and thereafter applying to said part a plurality of layers of metal including a layer of stressfree nickel, the improvement which comprises heat conditioning said part after said step of activation and prior to the application of said metallic layer, said heat conditioning comprising heating above 130 for at least 5 minutes.

2. In the process of metallizing a plastic part comprised of an acrylonitrile, butadiene and styrene resin by the steps of chemically conditioning, sensitizing and activating said plastic part, applying a layer of reduced metal and thereafter applying a layer of electrolytically deposited metal other than copper, the improvement which comprises conditioning said part through the use of an aqueous solution of molybdic acid in the range of about 5 to 10 grams/liter of water, phosphoric acid, sulfuric acid and a water-soluble dichromate salt in the range of over 15 grams/ liter of water, and applying a substantially stress-free nickel layer to said plastic part after the application of said reduced layer and prior to the application of said electrolytically deposited layer.

3. In the process of metallizing a plastic part comprised of an acrylonitrile, butadiene and styrene resin by the steps of chemically conditioning, sensitizing and activating said plastic part, applying a layer of reduced metal and thereafter applying a layer of electrolytically deposited metal other than copper, the improvement which comprises heat conditioning said part by heating it above 130 F. for more than 5 minutes after said step of activation and prior to application of said layer of reduced metal and applying a substantially stress-free nickel layer to said plastic part after the application of said reduced layer and prior to the application of said electrolytically deposited layer.

4. In the process of metallizing a plastic part comprised of an acrylonitrile, butadiene and styrene resin by the steps of chemically conditioning, sensitizing and activating said plastic part, applying a layer of reduced metal and thereafter applying a layer of electrolytically deposited metal other than copper, the improvement which comprises conditioning said part through the use of an aqueous solution of molybdic acid in the range of about 5 to 10 grams/ liter of water, phosphoric acid, sulfuric acid and a Watersoluble dichrornate salt in the range of over 15 grams/ liter of water; heat conditioning said part after said step of activation and prior to application of said layer of reduced metal; and applying a substantially stress-free nickel layer to said plastic part after the application of said reduced layer and prior to the application of said electrolytically deposited layer.

References Cited UNITED STATES PATENTS 12/1931 Corbit 204-19X 10/ 1934 Langdon 20419X 11/1948 Narcus 117-47 3/1959 Jendrzynski 106--1 1/1962 Waite et al. 204-49 7/1963 Radousky et al. 204-15 8/1967 Fischer 20448 JOHN H. MACK, Primary Examiner W. B. VANS'ISE, Assistant Examiner US. Cl. X.R. 

